Objective: Obesity is an independent risk factor for the development of atrial fibrillation(AF), and adversely impacts the success of catheter ablation procedures. This study evaluated the impact of body mass index(BMI) on the outcomes of surgical ablation of AF. Methods: Between 2003 and 2018, 250 patients underwent stand-alone Cox-Maze IV procedure(CMP-IV) for refractory symptomatic AF. Obesity was defined as BMI≥30kg/m2. Patients were divided into two groups: BMI<30kg/m2 (n=105) and BMI≥30kg/m2 (n=145). Freedom from atrial tachyarrhythmias(ATAs) was determined using electrocardiography, Holter, or pacemaker interrogation at 12 months and yearly thereafter. Recurrence was defined as any documented ATA lasting ≥30 seconds. Predictors of recurrence were determined using multivariable logistic regression. Preoperative and procedural characteristics and outcomes were compared among groups.Results: The obese patients had a higher BMI (36.1kg/m2 vs 26.2kg/m2, p<0.001), were younger (p=0.015), and had a higher rate of diabetes (p=0.013) compared to the non-obese cohort. There was no operative mortality in either group. There was no difference in perioperative characteristics including major postoperative complications (11/105 (11%) vs 11/145 (8%), p=0.500). During 3.2 ± 2.6 years of follow up, there was no significant difference in freedom from ATAs with or without antiarrhythmic drugs in obese patients when compared to the non-obese group (p > 0.05) (Figure). No predictor for AF recurrence was found.Conclusions: As opposed to catheter ablation, BMI was not a predictor of AF recurrence, and obesity did not adversely impact the outcomes of the CMP-IV. There was no increase in major complications in patients with higher BMI.